1. The field of art to which the invention pertains includes the art of electrical switching actuated by a pressure input.
2. Electrical switches adapted to operate in response to fluid pressures are widely used for an endless variety of industrial applications. Exemplifying pressure switches of the type commercially available is the disclosure of Gorgens et al U.S. Pat. No. 3,393,612 in which the switching mechanism is responsive to a single source pressure input. Likewise used widely are electrical switches operatively responsive to a pressure differential as might be used to operate a control function in correlation to a difference in pressure between taps such as, for example, those existing on either side of an orifice plate for measuring pressure drop across the plate.
In its simplest form, differential pressure switches of the prior art frequently employ a flexible diaphragm unit of sorts separating the opposing fluids as disclosed, for example, in U.S. Pat. No. 3,566,060. The respective pressures of each fluid are thereby permitted to bias the diaphragm in one direction or the other as a function of their net pressure differential. Sufficient movement of the diaphragm in either direction then operates via an actuating mechanism to effect appropriate triggering of an electrical switch mechanism with which it is associated. While operatively effective and appearing sound in principle, a significant drawback of such constructions is the potential mixing of pressures in the event of diaphragm failure. Still other differential pressure switch constructions are available which avoid the potential problem of fluid mixing through diaphragm failure by utilizing more costly features enabling the opposing fluids to be isolated by an intervening structure of substance. Exemplifying the latter are the disclosures of U.S. Pat. Nos. 3,626,813 and 3,751,988.